The Twelve Imams are the spiritual and political successors to Muhammad, the Prophet of Islam, in the Twelver or Ithna-‘ashariyyah branch of Shī‘ah Islam. According to the theology of Twelvers, the successor of Muhammad is an infallible human individual who not only rules over the community with justice, but also is able to keep and interpret the Divine Law and its esoteric meaning. The Prophet and Imams' words and deeds are a guide and model for the community to follow; as a result, they must be free from error and sin, and must be chosen by divine decree, or nass, through the Prophet. Imamate, or belief in the divine guide is a fundamental belief in the Twelver and Ismaili Shī‘ī branches and is based on the concept that God would not leave humanity without access to divine guidance. According to Twelvers, there is always an Imam of the Age, who is the divinely appointed authority on all matters of faith and law in the Muslim community. ‘Alī was the first Imam of this line, and in the Twelvers' view, the rightful successor to the Prophet of Islam, followed by male descendants of Muhammad through his daughter Fatimah Zahra. Each Imam was the son of the previous Imam, with the exception of Husayn ibn Ali, who was the brother of Hasan ibn Ali. The twelfth and final Imam is Muhammad al-Mahdi, who is believed by the Twelvers to be currently alive, and hidden till he returns to bring justice to the world.